Standard image sensors have a limited dynamic range of about 60 to 70 dB or less. For example, an 8-bit sensor, which generally is more affordable than sensors with greater bit depth, has a dynamic range of only 48 dB. However, the luminance dynamic range of the real world is much larger and natural scenes often span a range of 90 dB or more. When an image sensor captures a scene with a luminance dynamic range in excess of the sensor dynamic range, information is necessarily lost. Depending on the exposure settings, the brighter regions may be saturated and/or the dimmer regions may be underexposed, producing a captured image of a quality unable to reproduce the actual scene.
In order to simultaneously capture highlights and shadows of a scene, High Dynamic Range (HDR) technologies have been used in image sensors to increase the captured dynamic range. One of the most common techniques to increase the dynamic range is to merge multiple exposures, captured with a standard, low dynamic range image sensor, into a single HDR image that has a much larger dynamic range than a single exposure image. For instance, images of the same scene could be recorded at a series of different exposure times, where the longest exposure is set to optimally capture the dimmest portions of the scene and the shortest exposure is set to optimally capture the brightest portions of the scene.
Properly combining multiple images to form a high quality HDR image is challenging. The combination process involves, for each pixel in the HDR image, making decisions about the relative weight of the corresponding pixels in the input images. HDR images frequently contain artifacts due to flaws inherent to the image combination process. As an example, discontinuities may be apparent in areas of the image representing smooth intensity and/or color transitions in the actual scene, the discontinuities being caused by discrete shifts in the weighting of input images as a function of the properties of the input image pixels, e.g., intensity, noise, and sensor response.